In the related art, an insulating base made of ceramics such as an aluminum oxide-based sintered compact (alumina ceramics), for example, is used as a wiring substrate on which an electronic component is mounted and that is assembled in an electronic device. In the wiring substrate, a heat dissipation member may be embedded in the insulating base to improve a heat dissipation characteristic (for example, see Patent Literature 1). In such a wiring substrate, a surface metal layer may be disposed on the surface of the heat dissipation member and the insulating base.
As the heat dissipation member, for example, copper-tungsten (CuW) is used as a material that can be co-fired with the above-described alumina ceramics and has a thermal expansion coefficient close to that of the alumina ceramics. CuW is also used in the surface metal layer and a wiring conductor for co-firing with the alumina ceramics. However, when CuW is used as a material of the heat dissipation member and the surface metal layer, Cu of the surface metal layer moves to the heat dissipation member when firing, which causes a problem that the surface metal layer is not sintered.